This invention relates to the field of plastic containers. More specifically, it relates to the field of thin walled plastic containers used for liquids, such as water, milk, juice, detergents and the like. Frequently, such containers are formed by blow molding machinery. Such machinery introduces a tube of hot plastic between the faces of a mold. The mold faces are then closed and air is blown into the tube of plastic forcing it against the walls of the mold. Water cooling provided in the interior of the mold hardens the plastic in the shape of a container.
When the walls of the mold come together, some of the plastic is positioned beneath the mold area. This remains attached to the molded container by virtue of a narrow connective portion pinched between the walls of the mold. This excess material or tail flash is usually trimmed or severed from the container upon completion of the molding process.
Because the flash is not subjected to the same degree of cooling because of its mass, it remains hot after the container is freed from the mold. For the purpose of removing the flash the containers are positioned on their side and sent to an appropriate device for severing the flash. In standard containers of the type presently available the amount of plastic used to form each container is sufficient to insure that the tail flash is stiff enough that it does not flop over and touch the container when the containers are on their side. This is important because the flash is in a near molten state and will bond to the container and prevent the severing equipment from functioning properly.
In order to maintain plastic containers as an effective packaging medium, it is necessary to keep costs as low as possible and, where possible, further reduce costs. Todays plastic materials are sufficiently strong and ductile to be molded with very thin wall thicknesses. Thus, the materials presently available are capable of being formed into containers having wall thicknesses of 0.020 inches or less.
A problem encountered when extra thin walled containers are produced is that the amount of plastic in the tail flash is reduced in proportion to the reduction in wall thickness of the container. As a result, the tail flash is no longer sufficiently rigid to remain spaced away from the container and in the proper position for severing. In fact, it will rapidly flop over as the containers are turned on their side, engage and stick to the container bottom rendering the resulting container useless.
It is accordingly an object of the present invention to provide an improved mold and method whereby extra thin walled containers can be produced without interference from the tail flash sticking to the container bottoms.
It is another object of the invention to provide a mold for making extra thin walled containers having means for producing standoff projections in the tail flash and for cooling the projections so as to prevent sticking of the tail flash to the container prior to severing the flash therefrom.
A further object of the invention is to provide a method for molding extra thin walled containers such that the tail flash is positively maintained spaced from and at a predetermined angular orientation with respect to the bottom of the molded container.
A further object of the invention is to provide a method and apparatus permitting the manufacture of extra thin walled plastic containers having wall thicknesses of 0.020 inches or less.